1. Field of the Invention
The present invention relates to a recording and reproducing apparatus. More particularly, the present invention relates to a recording and reproducing apparatus which records and reproduces data on/from a holographic recording medium and has the function of diagnosing recording and reproducing components of the apparatus.
2. Description of the Related Art
There has been suggested a holographic recording method as a method for multiplexedly recording two-dimensional information on a single position. Holographic recording means that a same position on a recording medium is irradiated with reference light and information light, an irradiation angle and wavelength of the reference light are varied to generate different interferences, and different kinds of information are multiplexedly recorded on the single position on the recording medium (refer to Japanese Unexamined Patent Application No. 2004-158114).
Optical components such as a spatial optical modulator (SLM) constituted by a liquid crystal device, a beam splitter, an optical lens, a mirror and the like are employed for recording two-dimensional information (page data) on a medium. Further, a number of optical components such as a two-dimensional image pickup device constituted by a CCD or a CMOS, a optical lens, a mirror and the like are employed for reproducing the two-dimensional information recorded on the medium.
A holographic recording and reproducing apparatus for recording digital data constituted by documents, graphics and the like as two-dimensional information may become unable to record/reproduce data on/from a medium when there are slight malfunctions, defects or adjustment failures in any of the optical components including the spatial optical modulator (SLM) and the CCD.
For example, if there is a defect in a single pixel in the CCD, this may make it impossible to perform reproduction.
Therefore, when a SLM and a CCD are utilized in a holographic recording and reproducing apparatus, they are required to have no defect.
However, a spatial optical modulator and a two-dimensional image pickup device are components having a great number of pixels as many as several million pixels; therefore, it is difficult to constantly fabricate such components with no defect. Further, a CCD which had no defect at the time of purchase may suffer from defects during usage.
A holographic recording and reproducing apparatus employing a number of complex components has a higher possibility of suffering from failures or defects than that for a conventional medium such as a CD or DVD. If such failures and the like can not be early detected, large-capacitive two-dimensional data including partial defective data will be recorded, thus causing a user to waste time.
Further, a so-called write-once type holographic recording medium may largely lose its available recording capacity when defective data is recorded thereon. This may cause the medium itself to be wasted, thus causing significant monetary and psychological damages to the user.
Consequently, particularly in the holographic recording and reproducing apparatus, it is necessary to early detect malfunctions, defects and adjustment failures in the optical components such as the CCD.
Although holographic recording and reproducing enables performing multiplex-recording only by slightly varying the incident angle of reference light with respect to a medium, if the angle adjustment is only slightly deviated from a designed value, then desired two-dimensional data can not be reproduced. In such a case, it is difficult to identify whether the impossibility of reproduction of two-dimensional page data is caused by the angle adjusting mechanism, the medium itself or the reproducing system components such as the CCD.
Consequently, in the holographic recording and reproducing apparatus, it is particularly important to early detect defects and the like in the apparatus, and if the causes of such defects can be identified to some degree prior to carrying it to a maker for repairs, user-level adjustments may be performed in some cases without carrying it to the maker for repairs. For example, if it is possible to identify whether the impossibility of reproduction is caused by the apparatus or the medium and thus it has been proven that the medium has problems, then the apparatus itself can be used continuously.